Population connectivity of vulnerable Brazilian parrotfishes

Parrotfishes are iconic tropical and subtropical reef fishes, where they consume primary producers and contribute to reef bioerosion. Despite their ecological importance, parrotfishes have been threatened by overfishing worldwide. Understanding patterns of genetic diversity and connectivity is therefore essential for identifying conservation priorities and guiding management strategies for parrotfishes. Here, we evaluated the genetic diversity, connectivity, and gene flow of Sparisoma frondosum and S. axillare, two vulnerable and endemic Brazilian parrotfishes. A total of 104 samples of S. frondosum and 173 of S. axillare were collected along the Brazilian coast (from 00°50'S 44°15'W to 27°30'S 48°31'W). By assessing 11 microsatellite loci in S. frondosum and 16 in S. axillare, we found H_o < H_e; with strong structuring near the southern end of its distribution at the subtropical reefs of Rio de Janeiro state (RJ) for S. frondosum, and in the isolated Trindade and Martim Vaz Archipelago (IT) for S. axillare. No significant correlation was found between genetic differentiation and geographical distance, suggesting that factors other than spatial distance play key roles in shaping their genetic structures. Both species respond differently to marine barriers, and the observed patterns were discussed in light of how overfishing may be influencing genetic connectivity. Coastal populations require coordinated management along the Brazilian coast, while the genetic structuring in distant islands and at the southern range limits highlights connectivity constraints and potential vulnerability to environmental change.